1. Field of the Invention
The present invention relates to earth drilling equipment, in general, and, in particular, to a device for facilitating retrieval of a drill bit from crooked holes, soft rock or broken rock formations.
2. Description of the Prior Art
In the past, when drilling through somewhat crooked holes, soft rock or broken rock formations, there has been a tendency for a drill bit to become stuck or jammed upon attempts to extract the bit from the hole or formation. Centralizing devices for spacing the bit from the wall of the hole have been used as a means to solve this problem. However, such centralizers , which are attached above or "behind" the drill bits in typical drill strings, are at least as great in radial dimension as the bits themselves. Hence, such devices may in fact be successfully used to space a drill bit from a wall of a bore hole during and after drilling. However, by virtue of their size, such centralizers frictionally contact the walls of the bore hole and such frictional contact sometimes significantly increases the amount of energy and power required to remove the bit, the centralizer and the drill string from the hole.
Another conventional device which is mounted above or "behind" a drill bit in a drill string is a reamer. A reamer, being of greater axial dimension than the drill bit, is designed to enlarge the hole after the bit has bored the hole. As with centralizers, reamers may also be used to space a drill bit from a wall of a bore hole during and after drilling. But again, due to their radial size they also frictionally engage the wall of the bore hole and increased energy is required to remove such a reamer-equipped drill string from the hole. Still further, there are times when it is undesirable or even prohibited to enlarge the hole, e.g., for purposes of space conservation and/or other related considerations, to a diameter greater than that which was originally bored by the drill bit.
An advantage exists, therefore, for a device which has little frictional contact with a bore hole wall and can thus facilitate the removal of a drill bit from a crooked hole, a soft rock or a broken rock formation without enlarging the bore hole on the advancing or the retrieving trip of the drill string. A further advantage exists for a device which can preserve alignment of a drill bit during advancement or retrieval thereof through a crooked hole or a formation change while maintaining a minimum of contact between the device and the wall of the bore hole.
It is therefore an object of the invention to provide a device which facilitates retrieval of a drill bit from crooked holes, soft rock or broken rock formations.
It is a further object of the invention to provide a device for facilitating retrieval of a drill bit from a hole by virtually eliminating frictional contact between the device and the wall of the bore hole.
It is a further object of the invention to provide a device for facilitating retrieval of a drill bit from a hole while at the same time avoiding enlargement of the bore hole on either the advancing or retrieving trip of the drill string.
It is a still further object of the invention to provide a device for preserving alignment of a drill bit during advancement or retrieval thereof through a crooked hole or a formation change while maintaining a minimum of contact between the device and the wall of the bore hole.
Still other objects and advantages will become apparent when one considers the attached drawings and the description of the invention presented hereinbelow.